Brain Science: A Meditation on Mechanical Lie Detection

Drawing Inferences about "Deception" from Observed Events in the Brain:
Of fMRI and Similar Purported Tools for Observing or Inferring States of the Human Mind and Heart

Suppose that the levels (Level 1, etc.) shown in Figure 1 below are levels of the physical or material structure of the human brain.

Suppose that the small italicized letters below (f, g, etc.) represent events at a particular physical level of the brain; e.g., f may represent an electrical signal at a synapse.

Suppose that events of type f are observed at Level 1 and observations done to date shows that the pattern of f events at Level 1 occurs (or: has occurred, has been observed to occur) when deception occurs (or: has occurred, has been observed to occur, has been thought to occur).

What can one infer from those observations?
 
Figure 1

Suppose further that events at Level 1 in Figure 1 are determined by events at Level 2.

Does it matter for inferences about deception that events at Level 2 have not been observed in relationship to instances of deception?

Possibly.

It is logically possible that more that one pattern of events at Level 2 can produce the pattern of events at Level 1 but that only one pattern of events at Level 2 is related to observed instances of deception.

But the same relationship may hold between (i) events at any level and events at a lower level and (ii) events at any lower level and instances of deception. Thus, while only some patterns of events at Level 2 are associated with deception, the probative force of those patterns can in their turn fall victim to the (possible) fact that only one pattern of events at Level 3 is associated with instances of deception. These relationships may be repeated down to the "bottom," which in the above table are quantum processes and events. If so, invariant connections between events and instances of deception cannot be established unless and until observations of quantum level events have been observed.

But it is possible that the structure of the workings of the brain is more complicated (and, perhaps, also less bottom-up driven than is the case with Figure 1). It is possible -- is it possible? -- there are interactions between different Levels of the brain, interactions that affect the pattern of events at each Level of the brain. For example:


Figure 2

The interaction hypothesized in Figure 2 assumes that the processes at each level are not "deterministic" within each level. However, the logic of Figure 2 does not preclude the possibility that all the processes in Figure 1, taken together, are "deterministic" (even if only probabilistically so).

And then, of course, it is possible (is it possible?) there are interactions among different parts of the brain (which I will assume, for the sake of convenience, have four levels [though it is practically certain that each part of the brain has more than four levels of "existence"]):


Figure 3

If the sort of interaction shown in Figure 3 happens, inferences drawn from any pattern of events at Level 1 of Figure 1 cannot be drawn with certainty or, probably, even with near-certainty. (However, it does not necessarily follow that we learn nothing from observing events at Level 1 in Figure 1. Whether that's the case or not depends -- on many things.)

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The Hearsay Rule & Inference-on-Inference

Next January I am going to give a talk at the Institut fuer Rechtsphilosophie und Rechtsinformatik at the University of Munich (Ludwig-Maxmilians-Universitaet) in Germany about the hearsay rule. The prospect of giving this talk has forced me to think seriously about what I really think about the hearsay rule.

The hearsay rule is intermittently -- and perhaps regularly and periodically -- attacked as an abomination. Hearsay, it is often suggested, should be considered for what it is worth. That is what a rational person would do, it is often said. But when hearsay is in fact regularly received and considered in adjudication, the result is often a disaster. Consider the recent experiment with the "military commissions." It really did happen that the equivalent of a harmless goatherd was sometimes identified as a terrorist on the strength of an accusation by an absent (and often anonymous) accuser. Such experiments in hearsay rule-free proof suggest that there is usually less to hearsay than meets the ear.

A few years ago the 10th Circuit Court of Appeals suggested that although a prohibition against piling inferences on inferences is absurd, it is not absurd to require a proponent of evidence or a court to describe how inferences are piled on other inferences and what they reasonably amount to. See United States v. Summers, 414 F.3d 1287 (10th Cir. 2005). Perhaps the hearsay rule works in largely the same way: much hearsay ends up being admitted, but generally it manages to get admitted only if the proponent lays out a series of inferences that suggest that the hearsay in question is sufficiently probative to be admissible. Of course, it is true that some hearsay does not manage to get through even the very elastic and porous hearsay filter that our legal system uses; and this may mean -- it almost surely does mean -- that some trustworthy hearsay does not manage to find its way into trials. But a penalty-free injunction -- "Make a plausible argument for the probative force of your hearsay! That's all we ask." -- will have little or no effect in our adversary legal system. The occasional exclusion of reliable hearsay may be a price worth paying to get trial lawyers to assemble enough evidence to support a plausible argument for the probative value of the hearsay they decide to proffer.

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